Spray application of paints and functional coating materials onto surfaces of articles is a very well developed and industrially important activity. Very basically, the coating materials to be sprayed are fluids that contain curable components uniformly mixed with a liquid medium. The curable components may include solid particles or liquid. Once deposited onto the surfaces, the liquid medium typically evaporates and/or reacts alone or with curable components to leave a solid layer of a functional and/or decorative coating on the article.
Spraying involves moving a stream of the coating material fluid at a high flow rate through a relatively small diameter orifice of the applicator. Typically the nature and concentration of the curable components in the liquid medium is such that the spraying fluid has very high viscosity. Due largely to the generally high viscosity of the spraying fluid in painting and functional coating end use applications, more force than can be developed by portable manual methods is called for to achieve an effective spray for uniform coating.
Spraying of paint and functional coating materials virtually exclusively relies on power-driven or propellant-assisted techniques. Power-driven techniques utilize engine-driven or motor-driven pumps to hydraulically force the coating fluid through the narrow orifice at high pressure. Propellant-assisted techniques can use a compressed gas to mix with the coating fluid in the spray nozzle. As the gas expands during passage through the nozzle, entrained coating fluid atomizes to form droplets that are carried onto the surface being sprayed.
Power-driven and propellant-assisted spray application systems can be inconvenient in situations, for example, where small areas are to be coated or small quantities, especially small amounts of different colors or formulations of coating fluid are used. A practical example is touch-up painting in which a comparatively large coated area has had subsequent damage or was incompletely covered. Only a small surface area needs to be “touched-up” to repair the defect. Power-driven and propellant-assisted spray systems are typically large and employ power sources and auxiliary supplies, such as fuel. Consequently, moving such automated equipment to distant and remote locations, as is often necessary in military utilities, can be difficult and expensive. These paint systems also typically use large quantities of coating material and are not convenient for small area touch-up tasks. Moreover, these systems are reusable and should be thoroughly cleaned after each use. Cleaning has further drawbacks including extra investment of time, effort, personnel, cleaning materials, and the generation of waste. It is thus highly desirable to have a light, portable, manually operable spraying system for applying industrial quality paints and functional coatings. It is further needed to have such a portable, manually operable spraying system that is small enough for convenient application of paints and functional coatings in touch-up end use applications. A single-use, disposable spray application system that does not need cleaning after use is also needed.
The spray application of military equipment, and especially vehicles, with chemical agent resistant coating (“CARC” occasionally referred to herein as a “CARC coating”) is a particular end use application of great importance. CARC coating on surfaces of military vehicles is formulated to provide a variety of significant safety and strategic functions. Unlike ordinary protective coatings, a CARC coating is formulated to resist absorption of chemical and biological warfare agents. Consequently, CARC-covered apparatus such as military vehicles and equipment that are exposed to chemical and biological warfare agents can be relatively easily, quickly and thoroughly decontaminated, for example by simple washing.
CARC also provides both visual and non-visual camouflage protection. CARC is pigmented in colors selected to match the visual appearance of the surroundings in traditional manner to camouflage a coated object and thereby hinder detection by visual observation. Additionally, CARC composition includes infrared radiation (“IR”) signature management components. This aspect of CARC enables military equipment and vehicles to absorb and reflect IR radiation similarly to the natural surrounding environment. CARC-covered, synthetic equipment and vehicle surfaces mimic the background environmental IR signature and thus are more difficult to detect when scanned by extra-visual, IR radiation surveillance instruments. For example, a vehicle with a CARC coating that reflects woodland IR characteristics will be difficult to identify by IR surveillance sensor scanning when located in a heavily wooded environment. Furthermore, equipment effectively covered by CARC will have enhanced protection from many missile guidance systems that use IR signature as a primary target tracking method. Surfaces without CARC coating or with chipped, scuffed, scratched or other CARC coating defects will stand out from the surroundings and thus can be more readily detected by IR sensing surveillance instruments. A proper and full-coverage CARC surface enhances detection avoidance and is critical to survivability of personnel and strategic effectiveness in combat situations.
Military vehicles and equipment often experience rough treatment in service and their surface coatings are very frequently damaged when deployed in the field. Military and some civilian field locations are often distant from paint re-application stations. There is thus an important need to have a touch-up CARC coating application system suitable and available for use in remote military field service locations. Because field service locations can be primitive and lack mechanical and electrical infrastructure, automated spray paint application technology may not be practical in the field. A further need exists to provide light weight, portable and manually operable touch-up application system for CARC coatings that does not rely on a well-outfitted power and mechanical support system. Even in secure, well-powered, properly controlled and equipped coating stations, minor defects in CARC application requiring touch-up repairs can occur. A self-contained, portable, light weight touch-up CARC application system adapted for applying small amounts of CARC to repair small area defects in all locations is desirable to have.
It follows that CARC compositions are carefully formulated to provide the various functional features described above. It is very important that the CARC coating fluid being applied is of composition uniformly within critical specifications. CARC compositions, among other things, can include fine particulate solids dispersed in liquid medium. If not agitated, the heavy particles tend to settle in the coating fluid containers during long storage periods. Re-dispersion of settled solids into a uniform CARC composition in traditional storage containers can be difficult and nearly impossible without effectively intense agitation. The composition is also curable on exposure to ambient atmospheric conditions. If leakage of air or moisture into the CARC fluid containers during storage is permitted, non-uniformity of the composition in the container can easily occur. Storing CARC coating fluid in impermeable vessels with vapor- and liquid-tight seals is imperative. Opening the containers to redistribute settled solids into a uniform dispersion is deemed undesirable. It is extremely important that all CARC fluid applied, regardless of time in storage, has the complete complement of functional characteristics to effectively impart the intended visual and extra-visual camouflage performance. Stability and uniformity of CARC storage and application systems are of great concern.
It is highly desirable to have a portable, light weight CARC spray application system that enables enhanced re-dispersion of the composition uniformly consistent with all specifications after prolonged storage. It is much desired to have a self-contained, portable, manually operable CARC coating fluid spray application system that can easily provide a consistent quality, uniform CARC composition at time of application at remote locations in a touch-up coating repair situation after lengthy standing in storage.
An existing device for applying a touch up CARC coating is shown and described in U.S. Pat. No. 7,338,227, of Bullivant. That applicator uses a two component CARC coating fluid composition that employs mixing the components before application. It also applies the coating fluid via a roller applicator that requires contacting the surface to be coated with the roller. If the surface has acute angle features or if objects on the equipment are position too closely to the surface, the roller may not be able to contact the whole surface and thus will leave bare spots. A sprayed coating can reach crevices and other difficult to contact parts of complex-shaped articles. It is desirable to have a spray applicator that can distribute CARC coating fluid uniformly onto the complete surface.
Aerosol can applicators for paints are known. One such device is sold under the trademark PREVAL® (Chicago Aerosol, LLC). The PREVAL® sprayer unit includes a container with aerosol propellant and a plastic tube to take up the paint. The unit also has threads so that a plastic bottle containing a small quantity of paint may be attached to the PREVAL® sprayer unit. Certain paints can be sprayed as an aerosol from applicators such as this, however, the sprayer unit will not operate when held at an angle greater than 45° and it clogs easily. It has been difficult to use single component, moisture cure CARC coating fluid with a traditional aerosol container applicator. This type of coating cures by reaction with moisture which is difficult to exclude during the filling of aerosol cans.